The Galaxy S4 is an excellent device. Congrats on getting one. The S4 does not support the Mobile Life service which means that you will need to use Google, Samsung or one of the other account options that are available on the device to get your contacts to your device.
There is a way to make this process fairly simple for you. You'll want to export your MobileLIfe contacts so that you can import them to the back up server of your choice- I use Google because that's my Gmail account and all my people come to my new Android device every time. Use this link: http://support.t-mobile.com/docs/DOC-3003 to get the steps to export your contacts from MobileLife.
Once you've done that, sign in to your Gmail account, click Gmail in the left corner above your mailbox and choose contacts. When your contacts load, click More and then Import.